1. Field of the Invention
This invention relates to sealing of paperboard cartons in order to form an integral structural. Such structures of this type, generally, employ the use of radiation curable, pressure-sensitive adhesives and "spot curing" of the adhesives in order to seal and form the carton.
2. Description of the Related Art
Flap or end sealing of cartons following or prior to product filling has relied on the use of cold adhesives, hot melt adhesives or heat sealable polymer coatings. Typically, carton lines advance at a rate of 100 to 300 fpm.
It is well known that cold adhesives are incompatible with the higher speeds due to their extended set time requirements. Also, hot melt adhesives are limited to only certain end-use conditions due to temperature sensitivity. Finally, polymer coatings are costly, if applied as a continuous film and require specialized application equipment if patterned only in the seal areas.
The latest attempt to solve this problem is through the utilization of patterned-applied heat sealable coatings. This requires specialized printing equipment and powerful, inefficient heating systems to render the coatings tacky/sealable on the cartoning forming line. A reasonable amount of compression must also be applied to obtain an effective seal; therefore, proximity of the seal area and carton style are limited.
Finally, it is known to employ various sealing methods in order to seal various paper/paperboard materials together. Exemplary of such prior art are U.S. Pat. No. 4,605,578 ('578) to R. Emrich et al., entitled "Method and Apparatus for Connecting Together Material Plies Which are Unilaterally Thermoplastically Coated", U.S. Pat. No. 4,637,199 ('199) to R. S. Steck et al., entitled "Induction Sealing of Paperboard", U.S. Pat. No. 5,113,479 ('479) to A. Anderson et al., entitled "Method of Infrared Heating a Restricted Area on a Continuous Thermoplastic Laminated Web", and U.S. Pat. No. 5,498,304 ('304) to N. W. Shaw et al., entitled "Method of Manufacturing Corrugated Board Using A Thermoradiate Energy Source". While the '578, '199, '479, and '304 patents disclose various types of energy for sealing webs of material, such as hot air, induction heating, infrared heating and radiant heating, respectively, there is no disclosure of the use of ultra-violet (UV) light or adhesives which can be cured by UV light.
It is apparent from the above that there exists a need in the art for a carton sealing system which is capable of sealing cartons through simplicity of parts and uniqueness of structure, and which at least equals the sealing characteristics of the known carton sealing systems, but which at the same time is capable of utilizing the more efficient UW light.
It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.